1. Field of the Invention
The present invention relates to the leakage flux shielding structure of a flexible disk unit having a reduced thickness.
2. Description of the Prior Art
FIG. 8 is a diagram showing the positional relationship of the spindle motor, carriage assembly and stepping motor of a flexible disk unit of the prior art. FIG. 9 is a sectional view illustrating the positional relationship between the spindle motor and the carriage of the flexible disk unit. FIG. 10 is a diagram showing the whole configuration of the flexible disk unit. In these figures, reference numeral 1 represents a spindle motor for rotating a magnetic recording medium (unshown), 1a driving magnet, 1b starer, 1c coil, 1d spindle motor substrate, 1e chucking hub, 1f rotation axis, 2 frame, 3 carriage assembly, 3a carriage for mounting a magnetic head 3c, 3b arm for mounting a magnetic head 3d, 4 stepping motor for positioning the carriage assembly 3 in the radial direction of the medium, 5 sensor, 4a lead screw directly connected to the rotation axis of the stepping motor 4, 6 slide cam, 7 cartridge holder, 8 lever, 9 substrate, 10 shield cover and 11 front panel.
The operation of the flexible disk unit will be described next. In FIG. 10, when the magnetic recording medium (unshown) is inserted into the unit, the medium is loaded onto the read-write position by a loading mechanism consisting of the slide cam 6, the cartridge holder 7 and the lever 8. The detailed explanation of the loading mechanism is omitted here. When the medium is placed in the loading position, the hub of the medium is chucked by the chucking hub 1e of the spindle motor 1 fixed to the frame 2, and the medium rotates by the rotation of the spindle motor.
A projection (unshown) provided on the carriage assembly 3 is engaged with a groove in the lead screw 4a directly connected to the axis of the stepping motor 4 so that the rotary motion of the stepping motor is changed into the motion in the radial direction of the medium of the carriage assembly 3. Therefore, the magnetic heads 3c and 3d mounted on the carriage assembly 3 are moved in the radial direction of the magnetic recording medium by means of the stepping motor 4, and are positioned above the target truck. The flexible disk unit of the prior art is configured as shown in FIG. 8 and FIG. 9. That is, an outer rotor type spindle motor wherein the driving magnet 1a is located outside the stator 1b and the coil 1c is used, and the carriage assembly 3 is located above the stator 1b, the coil 1c and the driving magnet 1a as shown in FIG. 9.
Since the flexible disk unit of the prior art is configured as described above, the carriage 3 must be made thin to reduce the thickness of the flexible disk unit. However, the magnetic heads 3c and 3d can be made thin to a certain degree in connection with the unshown medium. Furthermore, there is a limit to a reduction in the thicknesses of the driving magnet 1a, the coil 1c and the case 1n of the spindle motor 1 in order to maintain performance. Similarly, the thicknesses of the IC 1h and the connector 1j on the motor substrate 1d cannot be reduced. Thus the disk unit of the prior art is difficult to be made thin.